Membrane roof structure

ABSTRACT

A membrane roof is adapted to assume a curved shape. The roof comprises a plurality of segments of steel each attached to the segment next adjacent it by a steel expansion joint member which is formed from a convoluted steel sheet. The membrane roof may be air supported, or it may be suspended, and in either case it assumes a curved shape; or it may be a floating roof in a tank, in which case it is substantially flat but is adapted to be suspended when the tank is emptied. The membrane is attached entirely around its periphery to a supporting structure which may be a substantially circular ring formed of a plurality of sections of steel pipe or a ring formed of reinforced concrete. Very wide clear span roofs may be constructed using the membrane roof.

United States Patent 91 Sinoski June 26, 1973 MEMBRANE ROOF STRUCTURE 22 Filed: Apr. 12, 1971 21 Appl. No.: 133,275

[5 6] References Cited 7 UNITED STATES PATENTS 10 1931 Paulsen 52 2 8/1942 Billner 52/127 2,355,248 8/1944 Stevens 52/80 2,872,933 3/1959 Mackey 52/2 3,029,971 4/1962 Reynolds"... 220/26 R 3,161,553 12/1964 Visser 52/2 3,302,358 2/1967 Jackson 52/573 2,587,353 2/1952 Marschak 52/82 3,221,451 12/1965 StOlZ 52/82 FOREIGN PATENTS OR APPLICATIONS 549,007 11/1942 Great Britain 52/573 534,204 10/1955 ltaly 220/26 SA OTHER PUBLICATIONS A Roof that Floats on Air; Sheet Metal Worker, July 1945, pages 41 and 42.

Roofs Supported by Air Pressure; American Roofer,

August 1944, pages 13, 23 and 24.

I Primary Examiner-John E. Murtagh Assistant Examiner-Henry E. Raduazo Att0rneyDouglas S. Johnson [5 7] ABSTRACT A membrane roof is adapted to assume a curved shape. The roof comprises a plurality of segments of steel each attached to the segment next adjacent it by a steel expansion joint member which is formed from a convoluted steel sheet. The membrane roof may be air supported, or it may be suspended, and in either case it assumes a curved shape; or it may be a floating roof in a tank, in which case it is substantially flat but is adapted to be suspended when the tank is emptied. The membrane is attached entirely around its periphery to a supporting structure which may be a substantially circular ring formed of a plurality of sections of steel pipe or a ring formed of reinforced concrete. Very wide clear span roofs may be constructed using the membrane roof.

14 Claims, 12 Drawing Figures PAIENIEnaunas ms 3.740.902

saw 1 or 4 INVENTOR. ONALD A. SINOSKI PATENTEDJUIIZB I975 INVENTOR. DONALD A. SINOSKI 1 MEMBRANE ROOF STRUCTURE BACKGROUND OF THE INVENTION liquid This invention relates to a membrane roof and supsupported from beneath by pressurized air alternatively which can be suspended from its periphery. In either case, the roof assumes a curved shape usually a portion of the surface of a sphere. Provision is made to permit the membrane roof to change its shape as it is inflated or suspended. However, provision is also made to provide control for pressurization equipment, when the roof is air supported, to maintain a substantially constant differential pressure across the membrane. The membrane roof may also be floated on a liquid such as oil; and in that circumstance, it would be substantially flat.

The membrane roof of the present invention is particularly adapted for use on domed structures where the rise of the roof is not great compared to its span. In its most common form, the membrane roof of this invention is an air supported roof whereby the membrane is supported by pressurized air at a higher gauge pressure than atmospheric pressure. As will be noted hereafter, the membrane roof is particularly suitable for wide span installations having a relatively low profile and clear span construction. Thus, the membrane roof of the present invention is suitable for installations of considerably greater size than has previously been contemplated; and further, the membrane roof of the present invention can be constructed for considerably lower cost per square foot of covered area than that of a roof having a fixed, rigid structure across its span width.

The membrane roof of the present invention is one which is relatively flexible. As will be noted, the roof is one which can be constructed on a substantially flat surface and then raised into position. Except when used as a floating roof, a roof according to this invention, when in position, may be suspended from a supporting structure around its periphery, or it may be air supported from beneath, as aforesaid. In either case, the roof assumes a curved shape as opposed to its substantually flat shape the curve usually being a portion of the surface of a sphere and means are therefore provided which permit flexing of the roof to an extent sufficient to assume an intended, predetermined curvature. In addition, the design of the structure accommodates differential pressure variations across the membrane as atmospheric pressure varies, and as well as to permit control of the supporting pressure when the roof is air supported so that by such control the intended curvature of the membrane roof can be maintained.

The membrane roof of the present invention is therefore adapted to such installations as large oil storage tanks having, for example, a 500 ft. diameter, or the membrane roof can be easily adapted to such installations as stadia for sports and other presentations, display pavilions, etc.

Wide span roofs have been constructed in a variety of ways. For example, the roof of a building, oil storage tank, etc., can be column supported, with rigid girders etc. being supported by the columns and supporting the roof covering. However, in many circumstances it has been desired that the roof be a clear span roof, i.e. a roof which is substantially free of columns and other supporting structure extending downwardly from beneath it. This criterion has been important in such diverse installations as storage tanks and stadia where the columns might obstruct the spectators view or might extend into a playing surface. Obviously, the cost of a clear span roof having a span in excess of several hundred feet, when the span is constructed with rigid, heavy girders, etc., supporting it, has been very high.

In some installations such as storage tanks, it is desirable to float a roof on top of the oil or other liquid being stored. In such a circumstance, the cost of a membrane roof according to this invention can be somewhat lower than that of floating roofs now being used; drainage problems etc., can be reasonably easily overcome, and sealing problems at the edge of the roof can be overcome with well known techniques. However, with present designs of floating roofs, provision must be made with columns which either project upwardly from the bottom of the tank or downwardly from beneath the roof to support it in the event that the tank is emptied, or otherwise the roof would collapse from its own weight when unsupported. Floating roofs, are, of course, only suitable for such installations as storage tanks.

Air supported roofs have been constructed wherein a thin membrane is supported from beneath by air pressure. Usually such roofs especially in large sizes exceeding several hundred feet have been textile, plastic or other flexible fabric. Unfortunately, the material used in the roof does not have sufficient tensile strength to withstand the forces involved in large spans when they are unsupported, and restraining cables are required to be placed over the fabric. Even with restraining cables, however, the profile of such roofs has been quite high, and relatively high internal air pressure has been required to provide stiffness of the roof against wind loading. One outstanding example of such a roof was the Pavilion of the United States of America at the International Exposition held in Osaka, Japan in 1970.

That roof was 460 ft. by 200 ft., with a rise at the centre of ft. and with a differential gauge pressure of 3 inches of water, and restraining cables over the roof at 20 ft. centres.

As noted above, means are provided to permit the membrane roof to assume a curved shape. An expansion joint is therefore provided between segments of the membrane roof, which expansion joint is at least partially convoluted when it is unstressed so that as stresses develop while the membrane roof assumes its curved shape, the expansion joint becomes less convoluted (essentially planar) and the change of shape of the membrane roof is therefore accommodated. Of course, provision is also made so that the membrane roof with expansion joints is substantially gas or liquid tight.

SUMMARY OF THE INVENTION next adjacent to it by an expansion joint member of material which is also adapted to be put in tension, so that the membrane roof is adapted to assume a curved shape. The membrane roof thus provided is therefore capable of being air supported or suspended from its periphery.

A further object of this invention is to provide a membrane roof having very large, clear span capabilities and one which can be relatively easily and inexpensively assembled and raised.

A still further object of this invention is to provide a method for assembling a membrane roof having a supporting structure where the supporting structure essentially comprises a plurality of relatively short pipe sections around the entire periphery of the roof whereby the assembly of the membrane roof is done on an ice surface.

Yet another object of this invention is to provide an enclosed structure suitable for use as a storage tank, and having a membrane roof adaptable to be air supported or to be floated.

A further object of this invention is to provide an enclosed structure suitable for use as a stadium or other large, enclosed structure, having a membrane roof which is air supported.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features and objects of the invention are more fully discussed hereafter in association with the accompanying drawings, in which:

FIG. 1 is a perspective, partially cut away view showing the main features of a closed structure having an air supported membrane roof in accordance with this invention;

FIG. 2 is a general cross-section across a diameter of a structure similar to that shown in FIG. 1;

FIG. 3 is a general cross-section of a structure across a diameter thereof, showing a roof similar to that shown in FIGS. 1 and 2 but with different supporting structure and sidewalls;

FIG. 4 is a general plan view showing a membrane roof in accordance with this invention;

FIG. 5 is a schematic diagram showing the action of roof segments as an air supported membrane roof according to this invention assumes a curved shape;

FIGS. 6A and 6B show the cross section of a typical expansion joint, as taken along the lines 66 in FIG.

FIG. 7 is a partial view showing several details of construction of a segmented membrane roof according to this invention;

FIG. 8 is a general cross-section view taken in the direction of arrows 88 of FIG. 7;

FIG. 9 is a further partial plan showing further details of construction of the segmented membrane roof according to this invention;

FIG. 10 is a view similar to FIG. 8 but showing the membrane roof according to this invention during a stage of its assembly, in accordance with one aspect of the invention; and

FIG. 11 is a general cross-section of a structure across a diameter thereof, showing a suspended membrane roof according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

An air supported membrane roof is shown at 10 in FIG. 1. The roof comprises a plurality of segments, each designated 12, and a supporting structure, wing overhangs, etc., which are discussed in greater detail hereafter and which are designated generally at 14. A central segment 16 is also shown.

The structure indicated in FIG. 1 is shown to have a vertical wall 18 which completely surrounds and encloses the volume substantially beneath the membrane roof 10. A plurality of columns 20 are found within the structure, as discussed in greater detail hereaftenAlso, enclosed by the roof l0 and wall 18 may be a sloping wall portion 22 and a substantially flat bottom 24, so that the volume enclosed beneath segmented membrane roof 10 and within wall 18 is also defined by the wall 22 and bottom 24. The precise details of the construction and configuration of the wall 18, the bottom 24 or the wall portion 22, are immaterial to this invention and may depend in great part on the purpose to which the structure, including the membrane roof according to this invention,is to be put.

For example, as discussed above, two of the more readily apparent uses to which a structure such as that indicated in FIG. 1 can be put are storage tanks and stadia for sports presentations, etc. Thus, the bottom 24 and the sloping wall section 22 indicated in FIG. 1 might be covered with a suitable liner, and the entire structure sealed in sufficient manner so as to comprise a storage tank for oil or other petroleum products, water, etc. On the other hand, the bottom 24 might be set out as a football field or a baseball diamond, and the sloping wall portions 22 might be equipped with suitable spectator accommodation so that the structure illustrated in FIG. 1 could be used as a sports stadium.

The structure illustrated in FIG. 2 is shown in very general schematic manner, and is essentially a crosssection of a structure such as that shown in FIG. 1. Like reference numerals indicate like structural integers or components. In the same manner, the structure illustrated in FIG. 3 is a general line-sketch similar to that of FIG. 2, except that the structure comprises a different general supporting structure 14 than that illustrated in FIGS. 1 or 2. In this case, the supporting structure 14 includes an earth filled dam 26 and a reinforced concrete ring 28; although the membrane roof 10 remains essentially the same as that used in the structure of FIGS. 1 or 2, as does bottom 24 and sides 22. In each case, it is anticipated that a configuration such as that which includes a bottom 24 and sloping side wall portions 22 would be achieved by earth excavation, back filling or a combination thereof. The earth filled dam 26 would normally be constructed using well known techniques. The structure shown generally in FIG. 3 is more suitable for use as a storage tank for oil or water than otherwise.

By way of example, as discussed above, and without in any way intending to limit this invention, structures such as those illustrated in FIGS. 1 and 2 and in FIG. 3 have been designed for use as oil storage tanks. In each case, a structure has been designed to have a substantially circular plan configuration, with a chord length of the membrane roof set at 500 ft. The rise at the centre of the roof membrane can be predetermined, as discussed hereafter; and the specific designs contemplate a gauge air pressure differential of l to 3 inches of water supporting the membrane roof, and at 32F, the rise is approximately l5.6 ft. In a structure such as that illustrated in FIGS. 1 and 2, where the height from the centre of the bottom 24 to the centre of the membrane roof 10 is approximately 80.6 ft. including a 15.6 ft. rise of the air supported membrane and considering a 40 ft. high wall or shell 18 the storage capacity is approximately 2.234 million bbls.

'( l2.3 l0 cubic feet storage capacity volume). Similarly, the structure of FIG. 3 having the same air supported membrane roof as that of FIGS. 1 and 2, and a height of 65.6 ft. from the centre of the bottom 24 to the centre of the membrane roof l0 including the rise of 15.6 ft. of the air supported membrane has a storage capacity of approximately 1.25 million bbls. (6.9 X cubic feet volume). The air supported membrane roofs illustrated in FIGS. 1, 2 and 3, when designed to have a chord length of 500 ft. (i.e. 500 ft. in diameter) and air supported, assume a curved shape which is a segment of the surface of a sphere whose diameter is approximately 4000 ft. Also, the arc length along the curve of the roof across a diameter thereof when the roof rise is 15.6 ft. is 501.31 ft. Since, as mentioned above, the diameter of the membrane roof the chord length is 500 ft., provision must be made to accommodate the increase of 1.3l ft. in arc length as measured along a diameter of the air supported roof. That provision is made, for the most part, by a plurality of sheet-like extension joint members as discussed hereafter.

FIGS. 4, 5, 6A and 6B illustrate the use of expansion joint members. Each of the expansion joint members is fitted to the segments which it attaches in such a manner that the edges of the segments can separate by a predetermined amount, and thus the radius of curvature of the segmented membrane roof can be predetermined. Thus, for any given installation, such as those shown in FIGS. 1, 2, 3 and 11, the amount of curvature of the roof and therefore the pressures required, the stresses induced and the load capacities can be determined for the most economical use of materials, etc.

FIG. 4 shows a segmented roof 11 having a plurality of segments 13. The inter-relationships of the segments when they are assembled in a flat plane is shown in solid lines, and the inter-relationship of the segments when in curvature is shown in broken lines. Thus, the

. inner ends of the segments 13 separate as at 19; and

as well, there is a radial separation between the inner ends 15 of segments 13 and the central segment 17, as shown at 21. Each of the separations between segments, and the amount of separation, is predetermined and is accommodated by an expansion joint.

Turning to FIG. 5, two segments 13 are shown, both when they are flat at 13a and when they are curved at 13b. The separation between the inner ends 15 is shown at 23, and between an inner end 15 and the central segment 17 at 25. It will be noted that the segments separate progressively further towards their inner ends; and it will be recalled that the outer ends 27 are substantially rigidly fixed to the supporting structure therefor, about which further details are discussed hereafter. It should also be noted that, in order for the roof to assume a substantially spherical curvature, some stretch of the metal comprising each of the segments 13 is provided for. This also allowsthe flat sheet of the segment to assume double curvatureso as to more closely approximate spherical curvature, and thereby so as to reduce stresses induced within the membrane and the supporting structure therefor.

An expansion joint 32 between two adjacent segments, portions of which are shown at 30a and 30b respectively, is shown in FIGS. 6A and 6B. The segments 30a and 30b are shown in FIG. 6A butted together at 31, and the ends 31a and 31b are shown separated in FIG. 6B, in which the expansion joint 32 is shown substantially flat. Because the segments 13 separate by a varying amount along the radially directed edges of any two adjacent segments, and because it is intended that the expansion joint 32 be placed and attached to the segments 13 so as to permit a specified and predetermined separation when the membrane roof assumes its curvature, the amount of expansion permitted by the expansion joint 32 between the segment 30a and 30b varies along its length. For example, at the inner end of segments 13 which are 200 ft. long, the expansion between segments permitted by the expansion joint 32 may be in the order of several inches, while near the outer ends 27 of such segments, the ex pansion permitted between them would be practically nil. Therefore, an expansion joint is placed to attach adjacent segments in such a manner that, when the intended separation between the joints is achieved at any point, the expansion joint is fully extended (i.e., essentially planar) at that point. The material of the expansion joint is one which is adapted to be placed in ten sion because it must accommodate the same tension forces as the segments of the roof. Also, it is preferable that the material be such that it will attempt to regain its original curvature in the event that the membrane roof is permitted to reassume its flat condition. Thus, preformed strips of stainless steel or spring steel may be used as expansion joint members, although mild steel or other suitable materials could be used. It is also necessary, of course, to instal an expansion joint member 36 (see FIG. 7) between the central segment 17 and the inner ends of each of the radial segments of the segmented membrane roof having the central segment 17. In that case, the material of the expansion joint member can be the same as before, as may best be determined by specific design considerations having regard to the dimensions of the roof, etc.; and in any event, with a circular roof the circumferential expansion joint 36 between the ends 15 of radial segments 13 and the central segment 17 would have a constant developed width when under full tension. Thus, a circumferential expansion joint can be easily preformed and installed, because the edges of the preformed metal strip (such as that illustrated by the convoluted shape of the expansion joint shown in FIG. 6A) are placed at constant width rather than at a changing width as they are along the length of a radially extending expansion joint. It should also be noted that the sideways separation between the radial segments such as 13, as they assume spherical curvature, is not directly linear in relation to the distance measured radially along a segment edge from one end thereof; and the edges of the preformed expansion joint are placed accordingly so that, when each expansion joint is developed it is substantially planar, and'the predetermined curvature of the roof is thereby achieved.

FIGS. 7 and 9 show several construction details of a portion of a segmented membrane roof according to this invention. A sea] 34 is shown at the inner and outer ends of each expansion joint 32, and may be made from a pliable, rubber-like material such as that sold under the trade mark I-IYPALON. The seals 34 are cemented to the roof segments and to the expansion joint members to seal any open gaps which may occur, such as between segments beyond the outer ends of the radially directed expansion joints 32 and at the inner corners thereof between them and the circumferential expansion joint 36, so that the roof is made substantially liquid and gas tight. Because the sealing membranes 34 are not structural integers with respect to the membrane roof structure and the stresses imposed therein, the material of the sealing membrane may be easily chosen because it has only to withstand the internal air pressure against it when installed in an air supported roof, or the downward directed weight of any water or snow loads that may lie on the membrane roof, particularly a suspended or floating roof.

The supporting structure for the membrane roof of this invention may vary from installation to installation, consistent with design requirements and principles. Thus, a supporting structure such as that illustrated in FIG. 3 may comprise an earth filled dam 26 and a reinforced concrete ring 28 to which the outer ends of each of the radial roof segments may be appropriately attached. As noted, the material of the membrane roof (usually steel sheeting) is adapted to be put in tension and is attached to the supporting structure so as to transmit forces thereto. Therefore, the supporting structure must be such as to withstand the forces which are transmitted to it.

A more usual supporting structure is indicated in FIGS. 1 and 2, and is discussed in greater detail hereafter with regard to FIGS. 7 to 10 inclusive. In the usual case, the supporting structure 14 comprises a plurality of steel pipe sections 38, each section of which has a substantially circular cross-section. The plan configuration of the supporting structure is substantially circular, and it can be appreciated that each of the pipe sections is straight, such as indicated in FIGS. 4 and 7 at the outer ends of each of the roof segments 13. A stiffening plate 40 may be installed across a diameter of the pipe section 38 so as to maintain it in circular cross-section when tensile forces of the membrane roof are transmitted to the supporting structure 14, and particularly to each pipe section 38.

The pipe sections 38 lie between a plate 42, beneath which is welded a U-channel 44, and a pair of superimposed plates 46 and 48 to which is welded a plurality of inverted T sections 50. An L section 52 is welded to plate 48 and to the ring 38 at the outer, lower portion thereof; and an L section 4 is welded to U-channel 44 and pipe section 38 at the inner, lower portion thereof. The structure is supported by a plurality of columns 20. Some of the columns 20 may also function as roof drains, as required. In such instances, suitable drain connections are provided through the plate 42, with a suitable outlet also being provided. Each column 20 is supported on a column footing 59.

An outer wall or tank shell 18 lies beneath the outer ends of plates 46 and 48 and T sections 50, and is supported at its lower end against a plate 56 on foundation or ring wall 58; and where the wall 18 comprises a tank shell, a sheet metal seal 60 is provided around the bottom of the tank shell between a steel liner 62 on the ring wall 58 and the tank shell. A storage tank which is filled with liquid is, of course, subjected to the usual hydrostatic pressures, with the result that provision is made by the use of the seal 60 to allow the tank shell 18 to move outwardly when acted upon by such pressures. The position of the tank shell 18 in an empty tank is indicated in FIG. 8 by the broken line at 18a. The roof segments 13 are attached to plates 43 which, in turn, are attached to plates 42. In all instances, the

means of attaching plates, sections, segments, etc., is conveniently by welding.

The ring which is formed by the plurality of pipe sections 38 may be pressurized to increase its stiffness, as is discussed in copending application Ser. No. 138,086 filed Apr. 28, 1971 and now abandoned.

A suspended roof is shown generally in FIG. 11 at 1 10. The tank walls or shell 1 18 is supported by a concrete ring wall 162, and the tank storage capacity is defined by the interior of the tank shell 118 together with tank bottom 124, sloping sidewalls 122, etc. The roof is essentially identical to the segmented membrane roof which has been discussed above, except as noted below.

A floating roof is most commonly provided for storage tank installations where the liquid being stored has high Reid vapour pressure so as to restrict evaporation of liquid, or for such liquids as sour crude oil whose vapours are particularly injurious to the material of the roof and for which direct contact of the membrane material with the liquid is desired. Provision is made by such as a cable to support ring 138 when the tank is emptied, as indicated by the broken lines in FIG. 11. When the tank is full of liquid, or indeed when the liquid level is above the lowest level permitted for the membrane and ring 138 by the suspension means 115, the floating roof lies with the undersurface of the membrane substantially across the upper surface of the liquid, with the ring 138 partially displaced into the liquid. A seal is provided at the outer edge of the ring 138 to provide a seal between the floating roof and the inner surface of the tank shell 118. A tank stiffening ring 132 is provided around the periphery of the tank shell 118 near its top.

Suitable roof drain means are provided, such as a drain sump 140 and a flexible drain line 142 so as to drain water from snow falls and rain falls away from the upper surface of the floating roof. In addition, suitable pump means are provided; and in the usual circumstance, oil having a specific gravity less than 1.0 is floated above water in the tank, and as oil is pumped therefrom more water is added so that the level of the membrane of the roof remains substantially constant.

When the roof is-suspended into an empty tank, its own weight causes the membrane to assume a spherical shape, which can be predetermined by suitable dimensioning of the segments and of the expansion joints provided therebetween. In any event, no elaborate and expensive supporting structure is required for the roof when it is not floating.

It has been mentioned that assembly of the segmented membrane roof of the present invention is most easily effected by placing all of the membrane segments on a flat surface and attaching them together by the performed expansion joint members. The outer periphery of the membrane segments is attached to the supporting structure in suitable fashion, as discussed above. Where it is possible, the terrain at which the roof is to be situated can be levelled, a suitable ditch or depression prepared for the lower half of the supporting ring when it is assembled of pipe sections, and the roof assembled. However, it is not always possible that the ground can be levelled over such a large working area as is contemplated for a membrane roof having a diameter of 500 ft., and the cost of scaffolding and temporary construction may be very high. In addition, where earch excavation is to be made as is contemplated in the figures accompanying this description it is easiest for the earth excavation to be done using large earth moving machinery so that the cost per cubic unit of earth removed may be low. However, it is contemplated that, especially in northern climates, a membrane roof according to this invention can be assembled on an ice surface during the winter season. Reference is made to FIG. 10 in the accompanying drawings.

The reinforced concrete ring wall 58 with the steel liner 62 attached thereto is flooded up to a level indicated at 64. Previously, of course, the concrete column footings 59 have been installed with plates 66 and rings 68 anchored thereto. A cable is attached to each ring 68 and is also attached to the ring structure 14 with sufficient slack so as to permit the ring to float upwards to its desired elevation during a later stage of the construction of the roof. To preclude the possibility of damage by ice expansion, a compressible pad 70 may be placed on the inside of the U-channel 44. When ice forms to a sufficient thickness to support the weight of the membrane roof and personnel and equipment working on it (somewhat in excess of six inches) insulation such as polystyrene sheeting 72 is placed on the ice, and the membranes 13 (and 17) are then placed on the insulating plastic. Thus, when welding operations are performed, heat transmission to the ice is sufficiently precluded. Heat transmission to the ice from the steel sheeting on sunny winter days is also precluded by the insulating sheeting 72.

When the membrane roof is assembled, including all of the segments thereof and all of the expansion joint members, and when the wall or tank shell is also assembled, the roof may be floated up to its final position by flooding beneath it with a sufficient volume of water to raise the roof to the desired level at which it can be secured. Hydrostatic testing of the tank may thereby be accomplished at the same time. Upon completion of the hydrostatic tests, and with the supporting structure 14 for the roof securely held, the tank can be drained. At this point the tank can be pressurized with air so as to inflate the roof, and the columns may be installed. Alternatively, where the segmented membrane roof of this invention is intended for installation in such structure as a sports stadium, it can be raised by pressurizing the volume beneath it with air.

The above discussion has been related to a segmented membrane roof which is adapted either to be air supported or suspended, and which assumes a curved shape when air supported or suspended. The membrane roof of this invention is adapted to be used as a floating roof having very high stability, and one from beneath which the liquid upon which the roof is floated may be removed and the roof suspended from its peripheral, supporting structure. The segmented membrane roof of this invention is intended to be made of material which is adapted to be put in tension, particularly sheet steel, so that high stiffness and low profile can be obtained. In addition, the membrane roof of this invention can be air supported with very low gauge pressure.

The membrane portion of the segmented membrane roof according to this invention, when air supported, is supported by the air pressure differential between the internal pressure and the ambient barometric pressure, which pressure differential may be approximately one to three inches of water gauge. The net pressure which imposes stress in the roof membrane is therefore the air pressure differential less the weight per unit area of the membrane. In order to achieve a constant net pressure within the structure over which the air supported membrane roof is placed i.e., constant differential pressure across the membrane thickness pressure control must be related to the membrane stress. This may be accomplished by such means as a roof stress sensing device which may comprise a strip of metal 74 (see FIG. 4) running over the roof and fixed at one end 76 to the supporting structure 14. The other end of the metal strip 74 is fixed to a spring 78 at 80, and the spring 78 is fixed at its free end 82 to the supporting structure 14; and the metal strip 74 is tensioned to the same tension as the material of the roof membrane. Any change in roof stress would therefore be sensed by differential movement between the end 80 of the metal strip which is attached to the spring 78 and the anchor point 82 for the spring. Suitable controls on air blowers, etc. (shown generally at 84), can therefore be easily provided. Any temperature variations would affect the material of the roof membrane and the material of the metal strip equally, and therefore the roof arc length, so that no additional temperature compensation for the roof stress sensing and the net pressure control would need to be provided.

A feature of the present invention is the provision of expansion joint members between adjacent segments, which expansion joint members are also of a material adapted to be put in tension, and which, in a preferred embodiment can be preformed of a material which will attempt to regain its original curvature. A method of construction of a segmented membrane roof according to this invention has been discussed.

A roof structure having a clear span of sufficient dimension that the roof could be placed over stadia suitable for public sports presentation and the like has been discussed above. In such an installation, the membrane roof would be air supported, but the roof is such that it may also be suspended with regard only to the design of the wall structures, etc., of the enclosure which would be required to support the weight of the suspended roof.

It is clear that the above discussion which is related to several specific alternative designs of a structure having a membrane roof according to this invention where in each case the flat, chord length of the membrane of the roof is 500 ft. and the roof is substantially circular in plan configuration is for purposes of illustration only. No dimensional limits or criteria are meant or implied.

Further, it is clear that the plan configuration of a membrane roof according to this invention need not be circular, and that if the material of the membranes and expansion joints is properly chosen, and the supporting structure designed for the stresses which will be imposed on it, any plan configuration of an enclosed structure having the membrane roof of thisinvention may be chosen.

In certain circumstances when the membrane roof is air supported, the columns 20 may be in tension and may therefore tend to lift. The mass of the column footings 59 is therefore chosen accordingly, so as to preclude such tendency and to maintain the structural integrity of the membrane roof and supporting structure.

Finally, it is clear that the shapes of the membrane segments, their number, and the presence or absence of centrally located segments, are matters of choice depending on the size of the structure, and other criteria. Expansion joint members may be radially directed, circumferentially directed around a central segment or a plurality of centrally located segments, etc., provided that each membrane segment is attached to each other membrane segment next adjacent it by an expansion joint member. The curvature of the roof when inflated or suspended is thereby predetermined.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In combination, a membrane roof and a supporting structure therefor;

said supporting structure being joined to said membrane roof substantially at the entire periphery thereof; said membrane roof including a plurality of radially directed segments of a material adapted to be put in tension, each of said segments" which is in contact with said supporting structure being attached to said supporting structure so as to transmit forces thereto;

each of said plurality of radially directed segments being separated from each segment next adjacent it respectively by a radially directed sheet-like expansion joint member of a material adapted to be put in tension; and each such expansion joint member which is in contact at its outer end with said supporting structure being attached thereto;

each saidradially directed sheet-like expansion joint member being secured along each side thereof to the respective one of said adjacent segments; each said sheet-like expansion joint member being at least partially convoluted when it is installed at its flat roof position, and less convoluted, essentially flat, when it is stressed in full tension so that said membrane roof may assume a predetermined curved shape with the outer periphery thereof defined at said supporting structure; and

a central segment of material adapted to be put in tension, said central segment being separated from the inner ends of each of said plurality of radially directed segments and the inner ends of each of said radially directed expansion joint members by a further, circumferential expansion joint member of sheet-like material adapted to be put in tension and which is secured to said central section around the circumference thereof and to said inner ends of said plurality of radially directed segments and said radially directed expansion joint members.

2. The combination of claim 1 further including a sheet of pliable, rubber-like material cemented at each place on said membrane roof where a gap occurs at the inner ends of said radially directed expansion joint members said inner ends and said circumferential expansion joint member, so as to make said entire membrane roof substantially liquid and gas tight.

3. The combination of claim 2 further comprising suspension means attached to said supporting structure and adapted to be put in tension so as to suspend said supporting structure and said membrane roof below said suspension means.

4. The combination of claim 1 where the material of each of said plurality of radially directed segments and said central segment is steel.

5. The combination according to claim 1 wherein the material of each of said plurality of radially directed segments and said central segment, and also the material of said radially directed expansion joint members and the material of said circumferential expansion joint members is, in each case, steel; and where each of said expansion joint members has a substantially flat portion along each side with a convolute formed therebetween, and said flat side portions overlie a portion of each segment on each side of each said expansion joint members and are secured thereto in surface-to-surface contact therewith.

6. The combination according to claim 5 where said supporting structure comprises a hollow steel ring formed of a plurality of steel pipe sections, and said membrane roof and supporting structure have a substantially circular plan configuration.

7. The combination according to claim 4 where said supporting structure is formed of reinforced concrete, and said membrane roof and supporting structure have a substantially circular plan configuration.

8. The combination of claim 6 where said supporting structure is pressurized.

9. The combination of claim 1 where said membrane roof is supported by pressurized air at a pressure beneath said membrane roof higher than atmospheric pressure at least sufficient to support the weight of said membrane roof.

10. The combination according to claim 9, further including gauge means, control means and air blower and supply means; wherein said gauge means is adapted to measure length differentials along an are taken on a diameter of said membrane roof and is connected to said control means and said air blower means to maintain substantially constant differential gauge pressure between the pressurized side of said membrane roof and atmosphere.

11. The combination according to claim 1 further comprising column means adapted to support the weight of said supporting structure.

12. An enclosed structure comprising a bottom, substantially upright walls and a membrane roof and a supporting structure therefor;

said supporting structure being, itself, supported from beneath and said supporting structure being joined to said membrane roof substantially at the entire periphery thereof;

said membrane roof including a plurality of radially directed segments of a material adapted to be put in tension, each of said segments which is in contact with said supporting structure being attached to said supporting structure so as to transmit forces thereto;

each of said plurality of radially directed segments being separated from each segment next adjacent it respectively by a radially directed sheet-like expansion joint member of a material adapted to be put in tension; and each such expansion joint member which is in contact at its outer end with said supporting structure being attached thereto;

each said radially directed sheet-like expansion joint member being secured along each side thereof to the respective one of said adjacent segments; each said sheet-like expansion joint member being at least partially convoluted when it is installed at its flat roof position, and less convoluted, essentially flat, when it is stressed in full tension so that said membrane roof may assume a predetermined 13 14 curved shape with the outer periphery thereof deradially directed expansion joint members. fined at said supporting structure and 13. The combination of claim 12 where said mema central segment of material p d to be P in brane roof and supporting structure therefor are sustension, said central segment being separated from pended by suspension means from the top of said the inner ends of each of said plurality of radially Stantiany upstanding wan means directed segments and the inner ends of each of 14. The combination of claim 12 where said said radially directed expansion joint members by b d b t t a further, circumferential expansion joint member rane too Is Suppone y pressure at a posmve difof sheet-like material adapted to be put in tension feremial gauge Pressure with respect to atmOsphere d hi h i secured to id central section around that the interior of said structure is pressurized with rethe circumference thereof and to said inner ends of pect o atmosphere.

said plurality of radially directed segments and said 

1. In combination, a membrane roof and a supporting structure therefor; said supporting structure being joined to said membrane roof substantially at the entire periphery thereof; said membrane roof including a plurality of radially directed segments of a material adapted to be put in tension, each of said segments which is in contact with said supporting structure being attached to said supporting structure so as to transmit forces thereto; each of said plurality of radially directed segments being separated from each segment next adjacent it respectively by a radially directed sheet-like expansion joint member of a material adapted to be put in tension; and each such expansion joint member which is in contact at its outer end with said supporting structure being attached thereto; each said radially directed sheet-like expansion joint member being secured along each side thereof to the respective one of said adjacent segments; each said sheet-like expansion joint member being at least partially convoluted when it is installed at its flat roof position, and less convoluted, essentially flat, when it is stressed in full tension so that said membrane roof may assume a predetermined curved shape with the outer periphery thereof defined at said supporting structure; and a central segment of material adapted to be put in tension, said central segment being separated from the inner ends of each of said plurality of radially directed segments and the inner ends of each of said radially directed expansion joint members by a further, circumferential expansion joint member of sheet-like material adapted to be put in tension and which is secured to said central section around the circumference thereof and to said inner ends of said plurality of radially directed segments and said radially directed expansion joint members.
 2. The combination of claim 1 further including a sheet of pliable, rubber-like material cemented at each place on said membrane roof where a gap occurs at the inner ends of said radially directed expansion joint members said inner ends and said circumferential expansion joint member, so as to make said entire membrane roof substantially liquid and gas tight.
 3. The combination of claim 2 further comprising suspension means attached to said supporting structure and adapted to be put in tension so as to suspend said supporting structure and said membrane roof below said suspension means.
 4. The combination of claim 1 where the material of each of said plurality of radially directed segments and said central segment is steel.
 5. The combination according to claim 1 wherein the material of each of said plurality of radially directed segments and said central segment, And also the material of said radially directed expansion joint members and the material of said circumferential expansion joint members is, in each case, steel; and where each of said expansion joint members has a substantially flat portion along each side with a convolute formed therebetween, and said flat side portions overlie a portion of each segment on each side of each said expansion joint members and are secured thereto in surface-to-surface contact therewith.
 6. The combination according to claim 5 where said supporting structure comprises a hollow steel ring formed of a plurality of steel pipe sections, and said membrane roof and supporting structure have a substantially circular plan configuration.
 7. The combination according to claim 4 where said supporting structure is formed of reinforced concrete, and said membrane roof and supporting structure have a substantially circular plan configuration.
 8. The combination of claim 6 where said supporting structure is pressurized.
 9. The combination of claim 1 where said membrane roof is supported by pressurized air at a pressure beneath said membrane roof higher than atmospheric pressure at least sufficient to support the weight of said membrane roof.
 10. The combination according to claim 9, further including gauge means, control means and air blower and supply means; wherein said gauge means is adapted to measure length differentials along an arc taken on a diameter of said membrane roof and is connected to said control means and said air blower means to maintain substantially constant differential gauge pressure between the pressurized side of said membrane roof and atmosphere.
 11. The combination according to claim 1 further comprising column means adapted to support the weight of said supporting structure.
 12. An enclosed structure comprising a bottom, substantially upright walls and a membrane roof and a supporting structure therefor; said supporting structure being, itself, supported from beneath and said supporting structure being joined to said membrane roof substantially at the entire periphery thereof; said membrane roof including a plurality of radially directed segments of a material adapted to be put in tension, each of said segments which is in contact with said supporting structure being attached to said supporting structure so as to transmit forces thereto; each of said plurality of radially directed segments being separated from each segment next adjacent it respectively by a radially directed sheet-like expansion joint member of a material adapted to be put in tension; and each such expansion joint member which is in contact at its outer end with said supporting structure being attached thereto; each said radially directed sheet-like expansion joint member being secured along each side thereof to the respective one of said adjacent segments; each said sheet-like expansion joint member being at least partially convoluted when it is installed at its flat roof position, and less convoluted, essentially flat, when it is stressed in full tension so that said membrane roof may assume a predetermined curved shape with the outer periphery thereof defined at said supporting structure and a central segment of material adapted to be put in tension, said central segment being separated from the inner ends of each of said plurality of radially directed segments and the inner ends of each of said radially directed expansion joint members by a further, circumferential expansion joint member of sheet-like material adapted to be put in tension and which is secured to said central section around the circumference thereof and to said inner ends of said plurality of radially directed segments and said radially directed expansion joint members.
 13. The combination of claim 12 where said membrane roof and supporting structure therefor are suspended by suspension means from the top of said substantially upstanding wall means.
 14. The combination of claim 12 where said memBrane roof is supported by air pressure at a positive differential gauge pressure with respect to atmosphere so that the interior of said structure is pressurized with respect to atmosphere. 